The subject matter described herein relates generally to wind turbines and to drive trains for wind turbines, and more particularly, to direct-drive trains of wind turbines and wind turbines with direct-drive trains.
At least some known wind turbines include a tower and a nacelle mounted on the tower. A rotor is rotatably mounted to the nacelle and is coupled to a generator by a shaft. A plurality of blades extends from a rotor. The blades are oriented such that wind passing over the blades turns the rotor and rotates the shaft, thereby driving the generator to generate electricity.
Some wind turbines utilize geared drive trains to connect the turbine blades to the electrical generators. The wind turns the blades mounted to a wind turbine rotor, which spin a low speed shaft, which feeds into a gearbox having a higher speed output shaft. This higher speed output shaft connects to a generator for producing electric power. The geared drive aims to increase the velocity of the mechanical motion.
Another type of wind turbines uses a gearless drive train which is also known as direct-drive train. In direct-drive train design, the wind turbine rotor and the generator are directly connected by a main shaft. Compared to geared drive trains, direct-drive trains required fewer components. Thus, wind turbines with direct-drive train are expected to be even more reliable. This is particularly important for offshore wind turbines where maintenance tends to be more costly. Direct-drive generators such as a synchronous generator operate at the same speed as the wind turbine rotor. Therefore, direct-drive generators are typically larger than the generators used in geared drive trains. Therefore, designing the structure for supporting the main shaft and the generator of direct-drive trains may require special consideration. Typically, a long main shaft transmits a torque between the wind turbine rotor and the generator and is supported by two bearings to effectively transfer non-rotational loads to a bed plate structure arranged in the nacelle. In this design, the long main shaft has to carry torque and bending loads and is thus comparatively heavy and expensive.
In view of the above, there is need for improved direct-drive trains for wind turbines.